Final answer:
Membrane carbohydrates are usually branched oligosaccharides found on the cells' exterior surface, crucial for cell recognition and determining blood types.
Step-by-step explanation:
Membrane carbohydrates are indeed usually branched oligosaccharides. On the exterior surface of cells, these carbohydrates are bound either to proteins, forming glycoproteins, or to lipids, forming glycolipids. These carbohydrate chains, which can be either straight or branched, consist of 2-60 monosaccharide units and play a critical role in cell recognition and cell adhesion.
These functionalities are crucial for the immune system to differentiate between body cells and foreign cells or tissues. The presence and type of oligosaccharides attached to the cell membrane determine the A, B, AB, or O blood types. It's also important to note that oligosaccharides begin their synthesis in the rough endoplasmic reticulum and are then further modified in the Golgi apparatus before being presented on the cell surface.